In Kolkata, prostitution is present in different forms. Prostitution may be brothel-based or non-brothel based as in the case of call girls. Although prostitution is not illegal in India, laws prohibit various aspects of prostitution, causing most prostitutes to work underground.
According to some sources the most common form of trafficking consists in offering false promises or some offer of help out of a dead-end or crisis situation, force is used later after the prostitutes have already been sold. "Mashis (brothel owners/older sex workers) use friendship, sympathy, also veiled threats to convince the women that it is now in their best interest to conform and begin working.” 
The largest red-light district in Kolkata is Sonagachi. The area came to be known as Sona Gachi from a sufi saint Sona Ghazi whose tomb (mazaar) is located in the locality. It is an area with several hundred multi-story brothels, and around 10,000 sex workers.  Sonagachi is located in North-Kolkata near the intersection of Chittaranjan Avenue Sova Bazar and Beadon Street, just north of the Marble Palace.
Several NGOs and government organizations operate here for the prevention of sexually transmitted diseases (STD) including AIDS. Sonagachi project is a prostitute's cooperative that operates in the area and empowers sex workers to insist on condom use; a relatively low percentage of prostitutes in this district (5.17% of the 13,000 prostitutes in Sonagachi) are estimated to be HIV positive. However, these efforts are hindered by human trafficking: men continue to demand sex without a condom, and women controlled by third parties are forced to oblige. Kolkata has emerged as a hub for the trafficking of girls, who often arrive from Nepal, Bangladesh and Burma. From Kolkata they are often sold again to brothels in Mumbai (Bombay). Some will go on to the Middle East, Africa and Europe. Many of the women in Sonnagachi were stolen from their homes; some were tricked and others sold into prostitution by their friends and families; most of them are illiterate.
According to some sources, prostitutes from Sonagachi who test HIV positive are not told about the results, and live with the disease without knowing about it "because the DMSC is worried that HIV positive women will be ostracized.” Some prostitutes in Sonagachi have stated that "the clients, at least three quarters of them" refuse to use condoms and “If we force them to use the condom, they will just go next door. There are so many women working here, and in the end, everyone is prepared to work without protection for fear of losing trade.”
In south Kolkata, there is a red light district in the famous neighbourhood of Kalighat. Though the location of this red light district is way too far-off from the sacred site of the famous Kali Temple but according to civic maps of the Kolkata Municipal Corporation it falls under the area of Kalighat.
Kidderpore is an area in the south of Kolkata. There is a small red-light district on Mushigunj Road, near The Statesman's printing press.
In Bowbazar, oppposite the 'Calcutta Medical College and Hospital' there is a small Shiva temple. The address is Premchand Boral Street. The small street left of this is another, small red-light district.
Baruipur is a small village south of Kolkata. There is small red-light district. A few stations away from Baruipur, there is a railway station named Shashan. There is a red-light area near the bazar or local market. There is also a red light area near Rambagan. Near the bazar in Behala Chowrasta, there was a red-light area, which was later stopped functioning, probably due to social pressure and lucrative residential/commercial complex promoting business. Also there was a red light area near the Khanna Cinema hall, north or Sealdah station, which was also stopped probably for the same reason. A few stations away from Sealdah station, there is a red light area in Naihati railway station near the river banks. South Kolkata Garia More(formerly) was an area. Right now it shifted little bit inside.
Street prostitutes work in Esplanade Crossing, opposite of cinema ‘Metro’ and in the street between Elite Cinema Hall and Regal Cinema Hall, Jagat Cinema near Sealdah station and under Sealdah flyover, and another place is Ultadanga flyover and railway foot over bridge, and Garia.
200KM far from Kolkata, the district head quarter of Murshidabad, Berhampore town also has a small red light district, 1 close to Laldighi area another prominent place is on Elite Hotel at NH34. Also a very small level high class escort service operates here,mostly college student or housewives or executives. Generally they use hotels booked by client or the flat of their pimp.
Sheoraphuli, a railway station few kilometers away from Kolkata, more precisely on the Howrah raiway track route, which is only a few minutes journey from Kolkata city, near the west bank of river Hooghly, also has a red light area. In Asansol, few kilometers away from Kolkata, a coal mining district town in West Bengal, there is a red light area in Lachhipur.
There are numerous private brothels and they are everywhere, but impossible to find without a guide. Maidan , in front of Victoria Memorial main gate some hookers are moving in evening.
One interesting point to highlight is that the police are aware regarding these prostitutes roaming in the streets of Kolkata, but in most of the time they intentionally harass the man with the prostitute for money, instead of saving the person.Even in Durgapur which is nearby Asansol and 170 KM away from Kolkata there is also a small red light area named Kadaroad near to main gate DSP.
Call girls operate independently and through pimps or escort agencies. Prostitution is operated from many beauty parlours and massage parlors in the city. Pimps (commonly called agents) in nightclubs, pubs, star hotels and floorboys acting as agents generally keep catalogue with pictures of the call girls. The girls operate in places like flats, hotels. etc. Generally the call girls go to the rooms in star hotels. However, when the client cannot provide a place of convenience, the agents provide one and the place is generally decided on before.
The Kolkata Police have connections with many call girls working as their informers. Many criminals like to spend time with the girls. Hence some call girls are used by the police to get information about suspected criminals.
Durbar Mahila Samanwaya Committee (DMSC), which runs the Sonagachi project and several similar projects in West Bengal, lobbies for the recognition of sex workers' rights and full legalization. DMSC hosted India's first national convention of sex workers on November 14, 1997 in Kolkata, entitled 'Sex Work is Real Work: We Demand Workers Rights'.